The present invention relates to a technology for controlling, based on a fresh air ratio, an internal combustion engine equipped with a variable valve operating apparatus which variably changes valve characteristics of intake and exhaust valves, such as, valve timing, a valve lift, an operating angle and the like.
There has been known an electronically controlled fuel injection apparatus called as a D-jetro type which determines a basic fuel injection quantity based on an engine intake pipe negative pressure and an engine rotation speed (see Japanese Unexamined Patent Publication 59-206624).
Further, there has been known a variable valve operating apparatus which variably changes valve characteristics of intake and exhaust valves, such as valve timing, a valve lift, an operating angle and the like. In a variable valve operating apparatus disclosed in Japanese Unexamined Patent Publication No. 10-068306, valve timing is controlled to be advanced/retarded by adjusting a phase of a camshaft relative to a crankshaft.
In the electronically controlled fuel injection apparatus of the above D-jetro type, the intake pipe pressure (boost pressure) is detected as a pressure obtained by putting a fresh air component pressure and a cylinder residual gas pressure together. In a case where an engine is equipped with a variable valve operating apparatus, since the valve characteristics of the intake and exhaust valves are changed so that the cylinder residual gas pressure is changed, even in the same intake pipe pressure, a fresh air component pressure out of the intake pipe pressure becomes indistinct depending on an operating condition of the variable valve operating apparatus. As a result, it becomes impossible to inject a fuel injection quantity corresponding to a real fresh air component pressure (fresh air ratio), causing a problem of deviation of an air-fuel ratio from a target value.
In order to solve the above problem, the present invention has an object to enable of obtaining, with high accuracy while suppressing an increase of data amount, a correction amount for correcting a fresh air ratio that determines operating amounts of an engine, in accordance with an operating condition of a variable valve operating apparatus.
In order to achieve the above object, the present invention is constituted so that, in an internal combustion engine equipped with a variable valve operating apparatus which variably changes valve operating characteristics of at least one of intake and exhaust valves, a control object is controlled as follows.
An intake pipe pressure of the internal combustion engine is detected by an intake pipe pressure detector, and an operating condition of the internal combustion engine is detected by an operating condition detector.
At a computing unit including a microprocessor and the like, a reference intake pipe pressure, and a reference fresh air ratio corresponding to a reference operating condition of the variable valve operating apparatus are computed based on the detection value of the engine operating condition, a fresh air ratio correction amount corresponding to an operating condition of the variable valve operating apparatus is computed based on the detection value of the intake pipe pressure and the reference intake pipe pressure, the reference fresh air ratio is corrected based on the computed fresh air ratio correction amount to compute a final fresh air ratio, and an operating amount of the control object in the internal combustion engine is computed based on the final fresh air ratio.
An operating device constituted of a fuel injection valve, an ignition plug, and driving circuits thereof operates the control objects, such as a fuel injection quantity, ignition timing and the like, by the operating amounts.
According to such a constitution, a reference operating condition of the variable valve operating apparatus, namely, the reference fresh air ratio in a case of assuming that valve characteristics, such as valve timing, a valve lift, an operating angle and the like are fixed, is corrected with the fresh air ratio correction amount computed corresponding to valve characteristics different from those in the reference operating condition of the variable valve operating apparatus, so that the fresh air ratio can be obtained corresponding to a change in a cylinder residual gas pressure due to the operating condition of the variable valve operating apparatus.
The fresh air ratio correction amount can be obtained with a few data amount using two parameters, the detection value of the intake pipe pressure and the reference intake pipe pressure. Thus, it is possible to improve accuracy of the fresh air ratio to be finally computed, and as a result, the fuel injection quantity, the ignition timing and the like can be controlled with high accuracy.
The other object and features of this invention will become understood from the following description with accompanying drawings.